New drugs for snakebite are desperately needed, say scientists, to replace the current 100-year-old treatment made by injecting snake’s venom into a horse and harvesting antibodies – which is very expensive, may not work and can cause lethal allergic reactions.
Snakebite, says the Wellcome Trust, is the cause of the world’s biggest hidden health crisis – and it is investing £80m in the hope of solving it. The World Health Organization will this month also launch a snakebite strategy aiming to halve deaths by 2030. Every five minutes, on average, 50 people are bitten by a snake. Between 81,000 and 138,000 people die from snakebite every year and about 400,000 are permanently disabled.
Although plenty of people are bitten in wealthy countries, it is those who live in poor communities, often working in the fields, who are likely to suffer most severely.
“Snakebite is – or should be – a treatable condition,” said Prof Mike Turner, Wellcome’s director of science. With access to the right antivenom there is a high chance of survival. While people will always be bitten by venomous snakes, there is no reason so many should die.
“Treatment has progressed little in the last century and it is too rarely accessible, safe and effective in the places where it is needed the most. It’s an incredibly challenging issue – there has been almost no investment in snakebite research over the last decade – but it’s also one that is solvable with support from WHO, national governments and other funders.”
The saw-scaled viper is generally thought to kill the most people. Russell’s viper is not too far behind, and is well known for causing kidney failure. The puff adder and Mozambique spitting cobra cause very bad tissue destruction. Taipans are generally regarded as having the most potent venom. The king cobra is the largest venomous snake but does not bite many people. The Gaboon viper has the largest fangs.
Antivenom is the only treatment and is a century old. Made from antibodies to venom which is injected several times into a horse, it will work for bites from the same type of snake but not necessarily any others. Antivenom exists for only about 60% of all the snakes in the world.
“Those you need in India may be quite different from Africa,” said Julien Potet, a neglected tropical disease adviser at Médecins Sans Frontières’ access campaign. “Snakes are different and venoms are different. Some species are not very well covered. That is a big problem the manufacturers have to address.”
Doctors and nurses may not be confident of the antivenom they have. “I was recently in Kenya. Healthcare providers were reluctant to use them because of the side effects. There is sometimes a high rate and they are severe,” he said.
Dr Philip Price, the snakebites science lead at Wellcome, said adverse reactions were a real problem. “Injecting horse proteins into people is not without risk,” he said. There can be severe reactions. “You can get a very serious form of anaphylaxis which can be fatal.”
They are also very expensive, costing about $160 (£125) a vial. A course could cost $800 to $1,600, while the total annual income of a farmer suffering a snakebite might be $200. “People don’t show up in hospital. They go to the local traditional healer,” he said. Those cases do not even show up in the figures, suggesting the problem is probably worse than we know.
Price said they needed to find new drugs that were not based on venom that would be useful across a whole range of snakebites and affordable for health systems in the developing world. Over the next seven years, Wellcome aims to develop new treatments, while bringing antivenom production into the 21st century, working with companies to make them better, safer and cheaper.
